The invention relates to aqueous electrophoretic lacquers capable of being deposited cataphoretically, which are curable by high-energy radiation and have the advantage of a good full cure even with high film thicknesses, and give good mechanical properties and, in particular, high resistance in an industrial gas atmosphere. It also relates to their production and use for the lacquering of electrically conductive substrates, e.g. of metal, electrically conductive plastic, e.g. metallised plastic, or electrically conductive coatings.
Coatings applied by the electrophoretic lacquer process have the advantage that they contain only a small quantity of residual water. The coating obtained does not therefore have to be pre-dried after rinsing off any bath material still adhering, but can be cured by high-energy radiation after possibly blowing off droplets of water.
In U.S. Pat. No. 4,039,414, compositions for the electrophoretic lacquer process are described containing a photoinitiator, dispersed in an ethylenically unsaturated polymer, dispersed in an aqueous phase, which can be deposited at a cathode and cured with TV radiation. In general, a number of acrylated polymers are mentioned, among which, as the only polyurethane acrylate, one that uses toluylene diisocyanate and polyether polyols as structural components is described. Lacquers on this basis have a tendency towards severe yellowing and towards early signs of degradation caused by weathering, leading to cracking, reduction in gloss and chalking, and also prove relatively brittle.
The invention was therefore based on the object of providing aqueous electrophoretic lacquers capable of being deposited cataphoretically, which do not exhibit these defects, which cure fully by high-energy radiation, even in high film thicknesses, and give lacquer films with improved properties compared with the prior art, particularly with regard to resistance in an industrial gas atmosphere, improved flexibility and good adhesion to the substrate.